U.S. Pat. No. 2,810,151 shows a caster composed essentially of three elements: a bearing block arranged to swivel eccentrically about a vertical axis; a wheel or roller arranged to turn on a horizontal axis; and a dished disc journaled on an inclined axis and arranged to provide, on its inner surface, a track on which the wheel rolls while the outer surface of the disc rolls on the ground.
As stated in U.S. Pat. No. 2,810,151, these casters were originally intended to use on dollies in refrigerator cars and cold storage rooms where their resistance to becoming caught in holes or between floor slats was thought to be useful. However, the prototypes of the casters made according to U.S. Pat. No. 2,810,151 failed to track or caster properly, as the importance of the geometric relationships disclosed herein were not then understood. When trial-and-error experimentation failed to produce acceptable results, the caster of U.S. Pat. No. 2,810,151 was shelved as impractical.
Not until recently, therefore, was further research undertaken in order to use this type of caster to solve a quite different problem: the moving of furniture on carpets, particularly on the deep-pile carpeting which is coming into increasing use in hotels and other commercial facilities as well as in homes. The present invention is directed to those geometric relationships of the caster design and to those configurations which allow the caster to maintain optimum tracking ability while solving the particular problems involved in the use of casters on carpeting as hereinafter described.